Forecasters said thunderstorms have already broken out in eastern areas, with intense storms forecast for Friday afternoon and evening across eastern parts of England and north-east Scotland into Saturday before fresher conditions make their way east across the UK for the weekend.

Will Lang, chief meteorologist at the Met Office, said: "The heatwave conditions are coming to an end but it's another hot day in the east and south-east of England today with temperature expected to reach 36C (96.8F) or 37C (98.6F) in places.

"If conditions all come together there's a 50% chance that we will break the July record temperature and a 20% chance of a new all-time UK record high."

A temperature of 36.7C (98F) at Heathrow on July 1 2015 is currently the record for the month of July, while the all-time record in the UK is 38.5C (101.3F) at Faversham on August 10 2003.

Mr Lang added: "Whilst many places will remain dry, the thunderstorms could lead to torrential downpours in places with as much as 30mm (1.2in) of rainfall in an hour and 60mm (2.4in) in three hours.

"Large hail and strong, gusty winds are also likely and combined could lead to difficult driving conditions as a result of spray and sudden flooding.

"There will also be some showers up the western side of the UK this evening and this heralds a more changeable and windy weekend."

Sunday will be a wet and windy day, with weather warnings issued for rain and gales.

Southerly winds will gust at around 35mph-40mph and up to 50mph for exposed coasts and hills, while rain will be most persistent over hills with parts of the Brecon Beacons and Dartmoor potentially seeing as much as 60mm-80mm (2.4in-3.2in) of rain, the Met Office said.

Tony Wafer, RNLI community safety manager, said: "If you are heading to the coast this weekend, please find out where your nearest lifeguarded beach is and ask the lifeguards for advice on conditions, especially if you are going in the water.

"RNLI lifeboats and lifeguards have had four times as many rescues of inflatables so far this summer than they did last year.

"They can be very dangerous and we urge the public to respect the water when having fun using inflatables this summer.

"Please do not use inflatable toys or kayaks in offshore winds or big waves. If you are at a lifeguarded beach, an orange windsock indicates offshore winds."